It is known that gallic acid and ester products thereof have the capabilities of skin whitening, antioxidation, impartment of stiffness and elasticity to hair and remedy of the hair damaged through coloring or by the action of a perm agent (remedy of F-layer and microfibrils). In fact, such a preparation has been expected for applications in various fields such as skin preparations for external use in the form of a cream or an emulsion, hair treatments such as hair styling agents or gels, and the like. However, gallic acid and its esters are usually poor in stability. In the course of actual preparation, a problem, which is coloration or precipitation, makes it difficult to show the functions or capabilities satisfactorily. In addition, some types of gallic acid esters are substantially insoluble in water, with the possibility that limitation is placed on the amount used.
In order to solve these problems, glucosylation of gallic acid and esters thereof wherein a saccharide is joined to the phenolic hydroxyl groups of gallic acid has been proposed (Japanese Patent Laid-open No. 2000-319116). Although such gallic acid glucosides are improved in solubility at normal temperatures, the solubility at low temperatures is so low that a problem arises in that when a solution of a gallic acid glucoside in water or a mixed solvent of water/polar organic solvent is allowed to stand at low temperatures, a precipitate is formed.
As described above, gallic acid glucosides are low in solubility in water or a mixed solvent of water/polar organic solvent at low temperatures, with the attendant problem that a precipitate settles.